Corrosion prevention



Patented Nov. 21, 1939 2,180,427 CORROSION PREVENTION Robert Wighton Moncrieff and Edward Boaden Thomas, Spondon, near Derby, England, assignors to Oelanese Corporation of America, a corporation of Delaware No Drawing. Application August 20, 1937, Serial No. 160,124. In Great Britain September 19,

1936 5 Claims.

This invention relates to a method of preventing or reducing the corrosive action of nonmetallic nitrogenous bases on metals and especially metals having a basis of iron.

We have found that metals having a basis of iron, for example cast iron, wrought iron and mild steel, although more resistant to nitrogenous non-metallic bases than many metals, do undergo corrosion by such bases and especially by relatively weak bases having a marked tendency to form metal-ammines, for example ammonia, pyridine, piperidine and quinoline, aniline and the substituted anilines, ortho-toluidine, ortho-phenylene diamine, diphenylamine and diamines, especially ap-diamines such as propylene diamine, butylene diamine and ethylene diamine. This corrosion is particularly evident in the presence of acid radicles, for example the acetic and other fatty acid radicles and the carbonic acid radicle. Since many of the bases referred to actively absorb carbon dioxide from the atmosphere, the carbonic acid radicle is almost invariably present unless special means are taken to exclude it. Baths which contain a non-metallic base together with a fatty acid salt of said base and. a certain proportion of carbon dioxide have a marked corrosive effect on iron and steel.

We have found that such corrosion can be reduced or substantially inhibited by the presence of metal compounds which are readily convertible into insoluble carbonates, especially alkaline earth metal compounds. Preferably the metallic compoundisawater-soluble salt of a weak acid, for example acetic acid, formic acid or other lower fatty acid, or a hydroxide. Thus for example the presence of small quantities of calcium acetate or hydroxide has been found to reduce very considerably the corrosive effect of warm solutions of ethylene diamine containing the corresponding acetate and carbon dioxide, on vessels and machinery of iron or steel. In view of the low solubility of calcium hydroxide this substance is preferably employed in the form of a suspension such as milk of lime. Among other metal compounds which can be used are: barium hydroxide, barium acetate, zinc acetate and lead acetate.

The method of the invention may be used, for example, in processes wherein cellulose acetate or other organic esters of cellulose are treated with aqueous solutions of organic bases to change their solubility properties, and in processes for stabilising and reducing the viscosity of nitrocellulose by treatment with aqueous solutions of bases such as pyridine or quinoline. Further applications of the method are in the treatment of cellulosic materials with organic bases in order to increase their afiinity for dyestuffs as described, for example, in U. S. A. application S. No. 140,893 filed May 5, 1937, and in the saponifying of organic esters of cellulose. The method is, in fact, broadly applicable Wherever metals having a basis of iron are exposed to the action of nitrogenous non-metallic bases such as are referred to above.

We have found that some degree of passivity against the action of such bases may be obtained by treating the metal with boric acid, e. g., heating the metal with an aqueous solution of boric acid for several hours in the presence of the organic base. This method is more successful with steels of high tenacity than with low grade steels. The invention includes carrying out such a pretreatment and then exposing the metal to the base in the presence of lime, calcium acetate or like acting substances.

The invention includes compositions containing the nitrogenous base and the substance which reduces or substantially removes the corrosive action which the composition would otherwise have on metals having a basis of iron. Thus, the invention includes compositions containing any of the nitrogenous bases referred to above, together with any of the corrosive-inhibiting agents.

The following examples illustrate the invention:

Example 1 A composition is made by adding to a 20-40% aqueous solution of ethylene diamine 1% of calcium acetate. This composition can be maintained in contact with cast iron or mild steel without substantial or serious corrosion occurring, even at temperatures in the neighborhood of 100 C. It is suitable for the treatment of regenerated cellulosic artificial silk to increase the afiinity for cotton dyes, as described in U. S. A. application S. No. 140,893 filed May 5, 1937, or for saponifying cellulose ester materials as described on U. S. A. application S. No. 752,376 filed November 9, 1934.

Example 2 A composition is made as described in Example 1 except that instead of calcium acetate calcium hydroxide is employed. This composition may be used for the same purposes as that of the pre ceding example.

Example 3 Artificial silk of regenerated cellulose of high tenacity, for example 2.5 to 3.5 or 4 grams per denier, is immersed in hank form in an aqueous bath containing of ethylene diamine and 142% of calcium hydroxide or calcium acetate. The treatment is effected for 10-15 minutes at ZG-GCP C. in iron vessels, after which the yarn is removed, washed and dried. It is found to have an enhanced afiinity for cotton dyes. During the process no substantial corrosion of the vessels occurs.

Example 4 Cellulose acetate artificial silk yarn of high tenacity is immersed in the composition described in Example 1 at a temperature of 40-60" C. for several hours, the process being carried out in a mild steel vessel. The process reduces the acetyl content of the material and is effected without substantial corrosion of the vessel.

Example 5 The process is carried out as in Example 4, except that calcium hydroxide is used in place of calicum acetate and is added slowly to the solution of ethylene diamine in the form of milk of lime during the process so as always to maintain a slight excess of lime in the bath. The result is similar to that of Example 4.

In a similar way compositions containing other nitrogenous bases, for example methylamine, benzylamine or other of the bases referred to above can be made having a reduced tendency to corrode vessels of iron or steel. In place of calcium acetate barium acetate may be employed. Similarly barium hydroxide can be used in place of calcium hydroxide. When the compositions of the invention are used in saponifying organic esters of cellulose, salts of the nitrogeneous base with the acid of the ester are formed in the saponifying bath. For example when the cellulose acetate materials are saponified the acetate of the organic base is formed. The presence of these salts renders it particularly advantageous to adopt the method of the invention for reducing or substantially avoiding corrosion, since in the absence of corrosion-preventing agents such salts appear to increase the normal corrosive action of the base on metals having a basis of iron.

Although the invention has been described with particular reference to the treatment of metals having a basis of iron it includes the treatment of other metals which undergo attack by nonmetallic nitrogeneous bases such as are specified above, particularly electropositive metals such as nickel, cobalt, manganese and chromium.

Having described our invention, what we desire to secure by Letters Patent is:

1. A liquid composition containing a nitrogenous base which normally has a corrosive action on iron and an alkaline earth metal compound which is convertible by aqueous carbon dioxide into a water-insoluble carbonate, said compound being present in an amount sufficiently to materially inhibit the corrosive action of the nitrogenous base on iron.

2. An aqueous composition containing in solution a nitrogenous base which normally has a corrosive action on iron and containng a watersoluble salt of an alkaline earth metal with a weak acid, said salt being present in an amount sufiicient to materially inhibit the corresive action of the nitrogenous base on iron.

3. An aqueous composition containing in solution a nitrogenous base which normally has a cor-- rosive action on iron and containng a hydroxide of an alkaline earth metal, said hydroxide being present in an amount sufiicient to materially inhibit the corrosive action of the nitrogenous base on iron.

4. An aqueous composition containing in solution ethylene diamine and calcium acetate, the calcium acetate being present in an amount sufficient to materially inhibit the corrosive action of the ethylene diamine on iron.

5. An aqueous composition containing in solution ethylene diamine and calcium hydroxide, the calcium hydroxide being present in an amount sufficient to materially inhibit the corrosive action of the ethylene diamine on iron,

ROBERT WIGHTON MONCRIEFF. EDWARD BOADEN THOMAS. 

